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Yield and soil system changes from conservation tillage in dryland farming: A case study from North Eastern Tanzania
Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Stockholm Resilience Centre. (Natural Resource Management)
Stockholm University, Stockholm Resilience Centre, Stockholm Environment Institute.
University of Zimbabwe.
Stockholm University, Stockholm Resilience Centre, Stockholm Environment Institute.
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2011 (English)In: Agricultural Water Management, ISSN 0378-3774, E-ISSN 1873-2283, Vol. 98, no 11, 1687-1695 p.Article in journal (Refereed) Published
Abstract [en]

Yield levels in smallholder farming systems in semi-arid sub-Saharan Africa are generally low. Water shortage in the root zone during critical crop development stages is a fundamental constraining factor. While there is ample evidence to show that conservation tillage can promote soil health, it has recently been suggested that the main benefit in semi-arid farming systems may in fact be an in situ water harvesting effect. In this paper we present the result from an on-farm conservation tillage experiment (combining ripping with mulch and manure application) that was carried out in northeastern Tanzania from 2005 to 2008, testing this hypothesis. Special attention was given to the effects on the water retention properties of the soil. The tested conservation treatment only had a clear yield increasing effect during one of the six experimental seasons (maize grain yields increased by 41%, and biomass by 65%), and this was a season that received exceptional amounts of rainfall (549 mm). While the other seasons provided mixed results, there seemed to be an increasing yield gap between the conservation tillage treatment and the control towards the end of the experiment. Regarding soil system changes, small but significant effects on chemical and microbiological properties, but not on physical properties, were observed. This raises questions about the suggested water harvesting effect and its potential to contribute to stabilized yield levels under semi-arid conditions. We conclude that, at least in a shorter time perspective, the tested type of conservation tillage seems to boost productivity during already good seasons, rather than stabilize harvests during poor rainfall seasons. Highlighting the challenges involved in upgrading these farming systems, we discuss the potential contribution of conservation tillage towards improved water availability in the crop root zone in a longer-term perspective.

Place, publisher, year, edition, pages
2011. Vol. 98, no 11, 1687-1695 p.
Keyword [en]
conservation tillage, ripping, agricultural droughts, water harvesting, maize yields, soil health
National Category
Agricultural Science Soil Science
URN: urn:nbn:se:su:diva-26825DOI: 10.1016/j.agwat.2010.02.013ISI: 000295764900002OAI: diva2:211487
Available from: 2009-04-15 Created: 2009-04-15 Last updated: 2011-12-30Bibliographically approved
In thesis
1. Traps and transformations: Exploring the potential of water system innovations in dryland sub-Saharan Africa
Open this publication in new window or tab >>Traps and transformations: Exploring the potential of water system innovations in dryland sub-Saharan Africa
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In semi-arid and dry sub-humid sub-Saharan Africa (SSA), high poverty levels and a heavy reliance on small-scale rainfed agriculture make rural livelihoods difficult. Upgrading current farming systems, in a way that safeguards productivity beyond field-scale, is urgent. This thesis builds on a case study of the Makanya catchment in Tanzania, and focuses on the potential of small-scale water system innovations (SWSIs), such as rainwater harvesting and conservation tillage, for increasing on-farm productivity while supporting multi-functional landscapes. The thesis consists of five papers that approach questions of alternative development trajectories for smallholder agro-ecosystems, and effects of SWSIs on key system variables, from varying perspectives. Paper I presents a conceptual model for interpreting multi-equilibrium dynamics in dryland agro-ecosystems, and analyzes Makanya's development over the past 50 years. Paper II investigates farmers' strategies to deal with drought and the impact of a local supplemental irrigation system on coping capacity. Paper III studies the effects of conservation tillage on yields and soil properties. Paper IV explores a set of future scenarios for the catchment. Paper V maps dryspell frequency and trends over time in a drylands-in-SSA perspective. The results show that smallholder farmers in agro-ecosystems such as Makanya depend on a wide array of on- and off-farm ecosystem services. The productivity of the surrounding landscape is especially important when crops fail. Furthermore, dryspells are a major constraint in these systems. In Makanya long dry-spells have become twice as common over the past 50 years, and frequently cause crop failures. This is a driver for land degradation, and maintains a climate-related poverty trap. SWSIs provide opportunities for dryland farmers to shift their agro-ecosystems to more productive trajectories through a number of mechanisms, including lowered crop failure frequency, altered on-farm water balances, and improved soil quality. Although this is promising, the task of transforming these systems is complex. For SWSIs to be effective, prerequisites are farming system solutions that integrate water- and nutrient management, and broad-based investments that focus on a much wider range of issues than only the water management technology. Moreover, given the uncertain future, investments in small-scale farming should be designed so that they benefit local communities across a range of pathways. Participatory scenario planning is useful both for identifying robust investment strategies and for navigating towards desirable development trajectories.

Place, publisher, year, edition, pages
Stockholm: Department of Systems Ecology, Stockholm University, 2009. 58 p.
smallholder farming, water system innovations, agricultural droughts, multi-functional landscapes, development trajectories, uncertainty
National Category
Natural Sciences
Research subject
Natural Resources Management
urn:nbn:se:su:diva-26833 (URN)978-91-7155-863-3 (ISBN)
Public defence
2009-05-15, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 13:00 (English)
Available from: 2009-04-24 Created: 2009-04-15 Last updated: 2009-04-16Bibliographically approved

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Enfors, ElinBarron, JennieRockström, Johan
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